Number of side number of triangle sum of the measure of the angles ​

Quadrilateral

#sides = 4

#∆ = 4-2 =2

sum= n(4-2)180° = 360°

pentagon

#sides =5

#∆ = 5-2 = 3

sum = n = (5-2)180° = 540°

Octagon

#sides = 8

#∆= 8-2 = 6

sum = n = (8 - 2)180° = 1080°

Nonagon

#sides =9

#∆ =9-2 = 7

sum = n=(9-2)180° = 1260°

Heptagon

#sides= 7

#∆= 7-2 = 5

sum = n= (7-2)180° = 900°

6mm^3 or .6cm^3

      216

      /   \

  36     6

  /   \     /

6     6   6

factor trees are nice.